lethargy vs languor

lethargy and languor both are nouns.

Word	Noun	Adjective	Verb	Adverb
lethargy	Yes	No	No	No
languor	Yes	No	No	No

As nouns, lethargy and languor are synonyms defined as:

Other synonyms of lethargy include flatness, phlegm, sluggishness.

lethargy (noun)	languor (noun)
weakness characterized by a lack of vitality or energy	inactivity; showing an unusual lack of energy
inactivity; showing an unusual lack of energy	a relaxed comfortable feeling
a state of comatose torpor (as found in sleeping sickness)	a feeling of lack of interest or energy
	oppressively still air